Page 25 - Geothermal Energy Renewable Energy and The Environment

Introduction 7

to serve. As an example, the following section discusses one such deployment venue—that of
generating electrical power—currently the most significant use of geothermal energy.

elecTrIcal demand and The characTerIsTIcs oF
GeoThermal enerGy

GeneraTinG elecTrical power for The Grid
The modern electrical grid has evolved over the last century to reliably supply power to an
increasingly complex market. The grid is a network that links together power generators and
power users through a system of transmission and distribution lines. In principle, a sophisticated
electrical grid can allow a customer on one side of a country to purchase power from a generator
on the other side of a country, or even another country, and reliably have that power provided on
demand. For historical and economic reasons, however, power grids are commonly segmented
into regions supplied and administered by operators and regulators. Such a system allows respon-
siveness to local and regional needs, while reducing transmission losses, and provides a mea-
sure of security from failures in the grid that could be catastrophically transmitted through
the network.
Such a system has several important characteristics and limitations. One characteristic is that the
demand or load on the grid will vary during the day. In a given region, the demand will be lowest
in the earliest morning hours and greatest at some point during the day or early evening. Seasonal
variability will influence the timing of the load and unusual weather can cause spikes in demand at
nontraditional times. Due to this variability, the concepts of baseload, peak load, and load follow-
ing have evolved and play an important role in designing grid components.
Baseload is the minimum amount of power a supplier must make available to its customers.
The amount of baseload power can vary from hour to hour, depending upon region and the power
demands that exist there. Usually a utility or power administrator will have a historical record and
contractual obligations on which to establish what the baseload demand will be.
The peak load is that load placed on the grid by the immediate conditions that are being expe-
rienced at that moment that exceed the baseload. Peak load can vary from day to day and month
to month. It can be strongly affected by such things as extremes in weather or local emergencies.
The capacity to meet this temporary increase in load that exceeds the baseload is called peaking
capacity. A power provider uses historical records to estimate what the likely peak demand will
be. It is on this basis that the maximum required generating capacity in a region is determined.
Generally, a utility or other provider will design the capacity of the local or regional system to
exceed by a few percent the estimated maximum possible peak load.
Load following is the ability to respond to changes in demand for power. Load following requires
the ability to increase power output on a time scale of minutes to tens of minutes. This can be
accomplished by either having generating plants capable of relatively rapid changes in power out-
put, or having in place contractual agreements to buy power on short notice from suppliers who can
quickly respond to demand changes.
Geothermal power plants are generally viewed as baseload power plants. In this sense they are
different from solar and wind power generating facilities, which are intermittent. Although all of
these facilities have the advantage that they do not require a fuel supply infrastructure to provide
energy, power generation from solar or wind facilities is interrupted (i.e., is intermittent) on a
diurnal and/or seasonal cycle and thus cannot provide baseload capability. In contrast, geothermal
energy never stops being supplied from the Earth’s interior and can thus be part of a baseload
supply system. Conversely, this also means that geothermal power is not well suited to provide
either load following capacity or peaking power, whereas solar or wind may be, depending upon